Mesa (master): glsl: fix glsl optimization infinite loop from copy_propagation_elements

[Eric Anholt]

Module: Mesa
Branch: master
Commit: 6c29452f38dacace4f234e9526bfdc1e23fb5051
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=6c29452f38dacace4f234e9526bfdc1e23fb5051

Author: Andy Clayton <q3aiml at gmail.com>
Date:   Thu Jan  5 21:17:53 2012 -0600

glsl: fix glsl optimization infinite loop from copy_propagation_elements

The trick was to produce an assignment in the IR along the lines of:

      (assign  (xyzw) (var_ref R0)  (swiz wwww (var_ref R0) ))

which occurs only rarely even in code that looks like it should do
this, because of the assignment temporaries generated in ast_to_hir.